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Floc 내로의 산소확산이 순산소활성슬러지 공정의 운전인자에 미치는 영향
최재환,김영진,김인수 ( Jae Hwan Choi,Young Jin Kim,In S . Kim ) 한국물환경학회 1997 한국물환경학회지 Vol.13 No.2
The effect of oxygen penetration into the microbial floc on the performance of activated sludge process was investigated. Two lab-scale completely mixed biological reactors maintaining dissolved oxygen (DO) concentrations at 2㎎/L and 10㎎/L were run under the same environmental conditions. For high DO level(10㎎/L), about 10% of additional reduced sludge production and slightly improved organic removal efficiency were observed compare to the low DO level(2㎎/L). In order to verify the difference of performance between the two completely mixed biological reactors, the diffusion model for oxygen transfer through bacterial floc was derived by adapting the concept that bacterial floc react as spherical porous catalyst. The data of oxygen uptake rate(SRT variation) used in the model was from the study of Clark et al (1971), and 100㎛ of floc diameter was assumed. The application of diffusion model. to the reactor operational data indicated that complete penetration of oxygen to the center of floc was occurred for the range of 1.0∼13day of SRT in the reactor of high DO level (10㎎/L). However, significant oxygen concentration drop was monitored according to SRT changes in the reactor of low DO level. In the case of low DO level, the concentration of active biomass calculated from the oxygen penetration model was lower than that of high DO level. In order to prove precisely the effect of D0 concentrations on the activated sludge process with diffusion model, it is recommended to measure the floc size and oxygen uptake rate in the future research.
Phenylethyl Tosylate 와 피라딘 및 N,N-디메틸 p-톨루이딘 과의 四級 암모늄鹽의 合成과 性質
최재환,여수동,Jae-hwan Choi,Soo-dong Yoh 대한화학회 1975 대한화학회지 Vol.19 No.5
Some quaternary ammonium salts were synthesized from 2-phenylethyl tosylate with pyridine and N,N-dimethyl p-toluidine, which were identified by NMR and IR spectrometry and the comparison of their physico-chemical constant has been made. It is found that the yield of the salts synthesized were significantly improved in acetonitrile rather than in acetone. 2-Phenylethyl tosylate를 피리딘 및 p-톨릴-N,N-디메틸아닐린과 反應시켜 대응하는 4級 암모늄鹽을 合成하여 NMR 및 IR로서 4級鹽을 確認하였고 그의 物理 및 化學定數를 比較하였다. 本實驗에서 얻은 2-phentylethyl pyridinium tosylate는 benzyl pyridinium tosylate와 마찬가지 方法으로 아세톤 중에서도 合成이 可能하나 아세토니트릴中에서 收率이 훨씬 좋음을 알았다.
축전식 탈염에서 전극반응에 의한 스케일 생성과 탈염성능에 미치는 영향
최재환 ( Jae-hwan Choi ),강현수 ( Hyun-soo Kang ) 한국공업화학회 2016 공업화학 Vol.27 No.1
The effects of scale formation of hardness material caused by electrode reactions on the desalination performance of the membrane capacitive deionization (MCDI) were investigated. During the repeated adsorption and desorption process for the influent containing Ca2+ ion, changes in effluent concentration and cell potential with respect to the number of adsorption were analyzed. It was found that OH- generation at the cathode was initiated at about 0.8 V or more of cell potential. In addition, the scale of Ca(OH)2 was formed on the surface of cathode carbon electrode by combining adsorbed Ca2+ ions and OH- ions generated from electrode reaction. As the scale was forming, the electrical resistance of carbon electrode was increasing, which resulted in the decrease of the adsorption amount. In the case of the operation at 1.5 V cell potential, the adsorption was reduced to 58% of the initial adsorption amount due to the scale formation.
펨토초레이저 백내장수술 도입 초기의 단기 임상경과 및고식적 백내장수술과의 비교
최재환(Jae Hwan Choi),양찬민(Chan Min Yang),정나연(Na Yeon Chung),임동희(Dong Hui Lim),정태영(Tae-Young Chung) 대한안과학회 2018 대한안과학회지 Vol.59 No.5
Purpose: To evaluate the short-term clinical outcome of femtosecond laser-assisted cataract surgery at the initial phase and to compare it with results from conventional phacoemulsification. Methods: This retrospective study was performed on 50 eyes who underwent femtosecond laser-assisted cataract surgery and 50 eyes who underwent conventional phacoemulsification. The short-term outcomes included uncorrected and corrected distance visual acuity and spherical equivalent. The complications of femtosecond laser-assisted cataract surgery were evaluated, and the prevalences of complications between the initial 25 eyes and latter 25 eyes of the cases were compared to evaluate the importance of the learning curve. Results: There were no significant differences in uncorrected (p = 0.78) and corrected (p = 0.89) distance visual acuity between groups 1 month postoperatively. There was no difference in spherical equivalent (p = 0.09). The phacoemulsification time was not different between groups (p = 0.15). However, there was a significant decrease in cumulative dissipated energy in the femtosecond laser-assisted cataract surgery group (p = 0.04). There were complications during femtosecond laser-assisted cataract surgery, such as subconjunctival hemorrhage, miosis, early entry corneal incision, and incomplete corneal incision. The prevalence of complications in the latter 25 eyes was less than that of the first 25 eyes treated with femtosecond laser-assisted cataract surgery; the prevalence of subconjunctival hemorrhage was reduced significantly (p = 0.02). Conclusions: The short-term clinical outcomes of the femtosecond laser-assisted cataract surgery group at the initial phase were not different, and in some cases, better than those of the conventional phacoemulsification group. A learning period is therefore required during the initial phase of femtosecond laser-assisted cataract surgery. J Korean Ophthalmol Soc 2018;59(5):419-427
유한 혼합 이변량 포아송 회귀모형에 대한 베이지안 추론: 호주 의료 서비스 자료에의 적용
최재환(Jae Hwan Choi),황범석(Beom Seuk Hwang) 한국데이터정보과학회 2022 한국데이터정보과학회지 Vol.33 No.3
셀 수 있는 이산형 자료에서 0이 과도하게 관측되는 자료는 다양한 연구 분야에서 흔히 나타난다. 이러한 자료에서 두 반응변수 사이에 상관관계가 존재하면 이변량 포아송 모형이 분석에 사용되며, 관측되지 않은 자료의 이질성을 고려하기 위해 랜덤효과를 포함할 수 있다. 특히 이변량 영과잉 자료의 과대산포 현상을 설명하기 위해 기존 모형이 확장된 유한 혼합 이변량 포아송 모형이 적용된다. 이 모형은 특수한 경우로 영과잉 이변량 포아송 모형을 포함한다. 본 논문에서는 두 반응변수 사이에 상관관계가 존재할 때 베이지안 추론 방법을 기반으로 랜덤효과가 포함된 유한 혼합 이변량 포아송 회귀모형을 제안하였다. 최적의 성분 개수를 가진 모형을 결정하기 위해 실제 호주 건강 설문조사 자료를 적용하여 다른 성분 개수를 가진 모형들과 비교한 후, 가장 적합한 모형을 기반으로 분석한 결과를 살펴보았다. Excess zero data are observed in various research fields such as social science, natural science, medicine, and engineering. In these data, if two response variables are correlated, we can consider a bivariate Poisson model and random effects may be included to take into account the heterogeneity of unobserved data. Furthermore, a finite mixture of bivariate Poisson models can be applied to explain the overdispersion of zero inflated data. We propose a Bayesian inference for the finite mixture of bivariate Poisson models with random effects when there is a correlation between the two response variables. In order to determine a model with the optimal number of components, the deviance information criterion was computed in the models. We applied the proposed model to the Australian health survey data, and checked the performance of the model.
축전식 탈염에서 정전압과 정전류 운전에 따른 질산 이온의 선택적 제거율 비교
최재환 ( Jae Hwan Choi ),김현기 ( Hyun Ki Kim ) 한국화학공학회 2015 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.53 No.3
The adsorption characteristics of ions were evaluated for the nitrate-selective carbon electrode (NSCE) in accordance with power supply methods. The NSCE was fabricated by coating the surface of a carbon electrode with anion-exchange resin powders with high selectivity for the nitrate ion. Capacitive deionization (CDI) experiments were performed on a mixed solution of nitrate and chloride ion in constant voltage (CV) and constant current (CC) modes. The number of total adsorbed ions in CV mode was 15% greater than that in CC mode. The mole fraction of adsorbed nitrate ion showed the maximum 58%, though the mole fraction was 26% in the mixed solution. This indicates that the fabricated NSCE is highly effective for the selective adsorption of nitrate ions. The mole fraction of adsorbed nitrate was nearly constant value of 55-58% during the adsorption period in CC mode. In the case of CV mode, however, the values increased from the initial 30% to 58% at the end of adsorption. We confirmed that the current supplied to cell is important factor to determine the selective removal of nitrate.